CSF2 and Crohn ileitis: Furthermore, GM-CSF-null mice have impaired gut barrier function and are prone to intestinal damage in models of murine ileitis (31, 32), while administration of exogenous GM-CSF ameliorates colitis in these models and promotes healing of the mucosal epithelial barrier (33, 34), further highlighting the importance of normal GM-CSF function for maintaining intestinal barrier integrity.